1. Field of the Invention
This invention relates to a metal thin film type magnetic recording medium of which magnetic recording layer is formed of a metal thin film.
2. Related Background Art
In recent years, with development of information processing technique and image processing technique, magnetic recording is increasingly demanded to have larger capacity and higher image quality. For responding to such demands, research and development have been actively done to obtain magnetic recording medium capable of high density recording. Particularly, as contrasted to the coating type magnetic recording medium generally employed at the present time, the metal thin film type magnetic recording medium having a ferromagnetic metal thin film such as Co, Co--Ni, Co--Cr, Co--O, etc. as the magnetic recording layer formed on a substrate by sputtering or vapor deposition is expected to be a promising medium suitable for high density recording.
On the other hand, also in still video system which is arousing a topic in these days, for the demands of its higher image quality and higher density recording, research and development about magnetic head, magnetic recording medium and signal processing, etc. have been progressed.
The magnetic recording medium to be used in still video system is for the time being a floppy disc of 2 inch in diameter, in view of the size, the weight which can be housed in an electronic still camera.
Also, since high frequency signals of several to ten and several MHz are utilized in the still video, recording and reproduction are performed by increasing the relative speed between the magnetic recording medium and the head. The speed conventionally used is 5.6 m/s (3600 rpm). Accordingly, when recording and reproduction are performed at a relative speed of 5.6 m/s by utilizing, for example, a high frequency signal of 7 MHz, the recording wavelength becomes 0.8 .mu.m. For performing recording and reproduction in such short wavelength region, the extent of contact between the magnetic recording medium and the head must be substantially uniform. If the interval between the medium and the head becomes nonuniform, spacing loss occurs during recording and during reproduction, which may cause reduction or fluctuation of output.
In still video, in order to maintain the interval between the magnetic recording medium and the head, the floppy disc is endowed with appropriate stiffness and, for example, as shown in FIG. 13, a pad (guide plate with a special shape) 7 is provided to make the disc 6 and the head 9 non-contact with each other by utilizing the air film created by high speed rotation of the disc 6. Further, 8 is a center core. By employment of such so called head pad constitution, prevention of abrasion of the magnetic recording medium and the head and stabilization of head touch of the magnetic recording medium can be effected, whereby improvement of durability of the magnetic recording medium and the head can be effected. As the floppy disc to be used for the head pad type electronic still camera, the so called coating type magnetic recording medium has been used in the prior art.
However, in order to make the electronic still camera itself compact by making the floppy disc compact or increase the number of photographable sheets in one sheet of floppy disc by increasing the recording capacity of one sheet of floppy disc, it is necessary to improve the recording density of the disc. If such improvement of recording density is attempted to realize by making the recording wavelength shorter, when the coating type magnetic recording medium (for example, one using CrO.sub.2, .gamma.-Fe.sub.2 O.sub.3, etc. in the magnetic layer) of the prior art is used, demagnetizing field within the magnetic layer becomes stronger as the recording signal becomes to have shorter wavelength to give rise to attenuation or rotation of residual magnetization, whereby there will ensue a problem that the reproduction output is markedly reduced.
Thus, it has been strongly desired to use a metal thin film type recording medium capable of high density recording as the floppy disc. However, no metal thin film type magnetic recording medium having good head touch with the magnetic head has yet been obtained, and when the metal thin film type magnetic recording medium is used as the floppy disc, abraded powder or flaw was generated on the surface of the medium or the head. For this reason, no excellent durability can be obtained in the metal thin film type floppy disc, whereby there has been the problem that the output is fluctuated.